The invention relates to a new adsorbent for the removal of metal contaminants from liquid and gaseous fluids, particularly hydrocarbon oils.
Typical crude oils may contain about 0.5 to 10 parts per billion (ppb) of mercury. Higher levels of mercury are often found in hydrocarbon condensates from natural gas production. Concentrations of between 50 and 300 ppb are commonly present in the condensates from some fields, but in condensates from certain fields can exceed 1000 ppb.
The heavy condensate produced from some fields contains about twenty percent C.sub.10 and higher hydrocarbons, and about five percent C.sub.20 and higher hydrocarbons. Typical crudes which often contain mercury are much heavier than the condensate, and can contain up to eighty percent C.sub.20 and higher hydrocarbons. When adsorbents are used to adsorb mercury directly, the non-selective adsorption of the heavy hydrocarbons competes too favorably with the mercury leading to low mercury adsorption capacity.
High levels of mercury in hydrocarbon liquids, crude oil, and condensates can cause problems in processing due to the corrosive effect of mercury on vital equipment such as cryogenic heat exchangers. Such heat exchangers are often made from aluminum which forms an amalgam with mercury. Other equipment can also be corroded by mercury. In addition, mercury can poison catalysts used to convert hydrocarbons to other organic compounds. Furthermore upon combustion, the mercury in hydrocarbon products is released into the air, causing environmental concerns.
A number of methods have been developed for removing mercury from gases and liquids. U.S. Pat. Nos. 4,094,777, 4,101,631, 4,419,107, 4,474,896, 4,909,926 and 4,946,596, and French Publication No. 2 310 795 disclose several such methods. For example, U.S. Pat. No. 4,094,777 and the French publication both employ a metal or metal compound supported by an adsorbent mass such as alumina or silica-alumina. U.S. Pat. No. 4,094,777 describes the use of copper sulfide (CuS) within the adsorbent mass, while the French publication indicates that the preferred metals are silver or a mixture of silver with gold, nickel or copper. U.S. Pat. No. 4,101,631 discloses a process that includes passing a mercury-containing gas stream through a sorption zone containing a crystalline zeolitic molecular sieve having elemental sulfur loaded thereon. U.S. Pat. No. 4,909,926 describes the use of CuS as an adsorbent at temperatures of about 450.degree. F. In this patent, mercury levels were reduced from about 200 ppb to below 10 ppb.
U.S. Pat. No. 4,474,896 discloses polysulfide adsorbents for mercury removal. These adsorbents employ any of a variety of support materials including ion exchange resins and zeolites. The adsorbents also include, as an essential component of the adsorbent complex, a metal ion bridging between the support and the sulfide. U.S. Pat. No. 4,496,596 also discloses adsorbents comprising metal sulfides on support materials.
U.S. Pat. 3,785,968 (hereinafter the "'968 patent") discloses the use of sulfur chemically bound to relatively low surface area polystyrene for heavy metals removal from hydrocarbon streams, specifically the removal of lead (Pb) from motor fuels. The '968 patent also discloses a method to produce these sulfur-polystyrene resin sorbents (hereinafter "S/resins") in which sulfur is dissolved in a high boiling solvent, such as a multi-chlorinated benzene, and the resin to be treated is suspended in the solvent while heating to elevated temperatures (170.degree. C.-220.degree. C.). The polystyrene resin employed by the '968 patent has a relatively low surface area, i.e., about 100 m.sup.2 /g.
The '968 patent provides no description of the utility of higher temperatures in the metals removal processes for rendering the process practical. The '968 patent also provides no indication that there would be an optimum level of sulfur content in the S/resin for maximum activity and/or capacity. In addition, the '968 patent provides no indication of the potential use of resins having higher surface areas, such as those unexpectedly found to be highly useful according to the invention.
Therefore, in order to overcome the disadvantages inherent in the prior art, it is a purpose of the invention to provide an economical process for effectively reducing metal contaminants, especially mercury, from hydrocarbon fluids to the low levels required for process equipment and environmental control.
It is also a goal of the invention to provide an environmentally sound process for metals depletion from hydrocarbon fluids.
Another purpose of the invention is to provide an improved metals removal process which can be readily integrated into existing processing systems.
It is still another purpose of the invention to provide an improved adsorbent for the depletion of metals, preferably mercury, from hydrocarbon fluids, which can be readily integrated into existing processing systems.
Yet another purpose of the invention is to provide a method for making an improved adsorbent for the removal of metals from hydrocarbon fluids.